The present invention relates to microwave phase shifters and, more particularly, to a novel microwave phase shifter utilizing high-density-interconnection (HDI) technology.
It is now well-known to shift the phase of the radiation emitted at each of a multiplicity of sites in an array, to steer a beam of that. radiation to a particular point in space and focus the beam steered thereto. The phase shift introduced at each array site is generally reciprocal, i.e. is imparted both to the transmitted energy to form the interrogating beam, and to the received energy to form a beam coherently obtained from only one location in space. The phase shifter should have minimal loss in both the transmission and reception conditions, to respectively maximize radiation efficiency (especially when large transmission powers are used) and to minimize reception noise figure.
One regime where low-loss phase shifters have been well received is in microwave phased array radar; a typical radar system may use several hundreds, or even thousands, of identical transmission/reception modules, each placed at one site in an ordered array of such sites, and all operating together, with individually-assigned and implemented module phase shifts, to form the transmission and reception microwave energy beam. One example of the required module is described in a June 1990 Final Report for an "Advanced L-Band Module" developed under U.S. Air Force Contract F30602-87-C-0188; the phase shifter here was implemented in a monolithic microwave integrated circuit (MMIC) which had low total yield--the visual yield was about 13%, even though the subsequent electrical yield was some what higher, at about 24%. It is highly desirable to provide a microwave phase shifter having a different construction, so as to improve the yield, while reducing the insertion losses of the circuit, to increase efficiency and minimize noise figure.